netdev - Re: [PATCH v2 net] r8169: fix NAPI handling under high load

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Message-ID: <20181019215614.GA14941@electric-eye.fr.zoreil.com>
Date:   Fri, 19 Oct 2018 23:56:14 +0200
From:   Francois Romieu <romieu@...zoreil.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net] r8169: fix NAPI handling under high load

Eric Dumazet <eric.dumazet@...il.com> :
> On 10/18/2018 03:59 PM, Francois Romieu wrote:
> > Eric Dumazet <eric.dumazet@...il.com> :
> > [...]
> >> One has to wonder why rtl8169_poll(), which might be called in a loop under DOS,
> >> has to call rtl_ack_events() ?
> > 
> > So as to cover a wider temporal range before any event can trigger an
> > extra irq. I was more worried about irq cost than about IO cost (and
> > I still am).
> > 
> Normally the IRQ would not be enabled under DOS.

Yes.

My concern was not the DOS situation when NAPI runs at full speed.
As far as I was able to experiment with it, the driver did not seem
too bad here.

The location of the ack targets the interim situation where the IRQ
rate can increase before NAPI kicks in. By increasing the time range
whose events can be acked, the maximum irq rate should be lowered.

-- 
Ueimor